Process and catalyst for preparing C2-oxygenates from synthesis gas

ABSTRACT

In a process for preparing C 2 -oxygenates by reaction of CO and H 2 over a rhodium-containing supported catalyst, the catalyst comprises, based on the total weight,  
     from 0.01 to 1O% by weight of rhodium,  
     from 0.001 to 10% by weight of zirconium,  
     from 0.01 to 5% by weight of iridium,  
     from 0.01 to 10% by weight of at least one metal selected from among copper, cobalt, nickel, manganese, iron, ruthenium and molybdenum,  
     from 0.01 to 10% by weight of at least one alkali metal or alkaline earth metal selected from among lithium, sodium, potassium, rubidium, magnesium and calcium, on an inert support.

[0001] The invention relates to a process and a catalyst for preparingC₂-oxygenates from synthesis gas, i.e. CO/H₂ gas mixtures.

[0002] The heterogeneously catalyzed conversion of synthesis gas intohydrocarbons (Fischer-Tropsch synthesis) or into methanol has been knownsince the 1920s. It was discovered only in 1975 that rhodium catalystscan convert synthesis gas L directly into C₂-oxygenates.

[0003] In principle, the direct reaction of synthesis gas over rhodiumcatalysts can lead to a broad range of products. Thus, methane andhigher hydrocarbons and also oxygenates such as methanol, ethanol,higher alcohols, diols, acetaldehyde and acetic acid are formed overunpromoted Rh/SiO₂ catalysts. Both the selectivity and the activity ofrhodium catalysts can be considerably modified by doping with otherelements or by appropriate selection of the support. For example, dopingwith lithium or potassium serves to suppress methane formation, dopingwith manganese gives a considerable increase in activity without theselectivity being significantly influenced, and the use of CeO₂ insteadof SiO₂ as support results in a significant increase in the selectivityof ethanol formation. Furthermore, the product distribution depends onreaction parameters such as pressure, temperature, conversion and CO/H₂ratio.

[0004] EP-A-0 010 295 describes a process for preparing ethanol fromsynthesis gas, in which the reaction is carried out over a supportedrhodium catalyst comprising, as cocatalyst, one or more of the elementszirconium, hafnium, lanthanum, platinum, chromium and mercury. EP-A-0079 132 relates to a process for preparing oxygenated hydrocarbons bycatalytic reaction of synthesis gas over a supported catalystcomprising, as active components, rhodium, silver, zirconium andmolybdenum and also, if desired, iron, manganese, rhenium, tungsten,ruthenium, chromium, thorium and potassium. The preferred supportmaterial is silicon dioxide. J5 9078-130-A relates to a process forpreparing acetic acid, acetaldehyde and ethanol by reaction of synthesisgas over a rhodium catalyst comprising manganese, zirconium and at leastone alkali metal as promoters.

[0005] The direct, heterogeneously catalyzed gas-phase synthesis ofacetic acid from synthesis gas over rhodium catalysts has beenintensively researched, especially in the years 1980 to 1986 as part ofthe Japanese C₁ project “Research and Development Program for NewTechnologies to Produce Basic Industrial Chemicals from Carbon Monoxideand other Chemicals”. During the course of this work on the synthesis ofacetic acid, the influence of about 60 elements as promoters on theactivity and selectivity of heterogeneous rhodium catalysts wassystematically examined. It was found that promoters such as Mg, Sc, Ti,V, Cr, Mn, Mo or La increase the catalytic activity, while promoterssuch as Li, K, Zr or Ir lead to an increase in the selectivity of aceticacid formation. At the end of the project, an optimizedRh-Mn-Ir-Li-K/SiO₂ catalyst enabled an acetic acid selectivity of 71% tobe achieved at a space-time yield of 344 g/l*h. A further catalyst whichwas not described in more detail but gave an overall selectivity toacetic acid +acetaldehyde of 90% at a space-time yield of 480 g/l*h wasalso developed.

[0006] The results of the Japanese C_(l) project have been compiled inthe book “Progress in C_(l) Chemistry in Japan”, Elsevier, 1989, withspecifically the work on the preparation of acetic acid from synthesisgas being described in Chapter 6 (pages 287 to 330). In the screeningtests on catalyst optimization, not only was the influence of variouspromoters on the catalyst performance elucidated, but a number offurther parameters such as the test conditions (P, T, SV, CO/H₂ ratio),partial poisoning with sulfur, the support composition and porestructure, the Rh particle size and the conditions in the drying and thereduction of the catalyst were also examined. In addition, the reactionkinetics over an Rh-Mn-Ir-Li-K!SiQ₂ catalyst and the ageing behavior ofan Rh-Mn-Ir-Li/SiO₂ catalyst were examined.

[0007] It is an object of the present invention to provide a process anda catalyst for preparing C₂-oxygenates, which give the desired productswith high conversions and high selectivities at a high catalyst activityand operating life.

[0008] We have found that this object is achieved by a process forpreparing C₂-oxygenates by reaction of CO and H2 over arhodium-containing supported catalyst, in which the catalyst comprises,based on the total weight,

[0009] from 0.01 to 10% by weight of rhodium,

[0010] from 0.001 to 10% by weight of zirconium,

[0011] from 0.01 to 5% by weight of iridium,

[0012] from 0.01 to 10% by weight of at least one metal selected fromamong copper, cobalt, nickel, manganese, iron, ruthenium and molybdenum,

[0013] from 0.01 to 10% by weight of at least one alkali metal oralkaline earth metal selected from among lithium, sodium, potassium,rubidium, magnesium and calcium, on an inert support.

[0014] It has been found, according to the present invention, that theabove catalyst displays a very good performance spectrum in theconversion of synthesis gas into C₂-oxygenates. The catalyst displays ahigh activity and selectivity, even when the rhodium content is verylow.

[0015] The catalyst support is preferably selected from among SiO₂,Al₂O₃, TiO₂, zeolites, activated carbon, diatomaceous earth and mixturesthereof.

[0016] The alkali or alkaline earth metal or metals is/are preferablyselected from among lithium, potassium and magnesium.

[0017] The metal or metals is/are preferably selected from among copper,manganese, iron, ruthenium and molybdenum.

[0018] A preferred catalyst comprises

[0019] from 0.1 to 5% by weight, in particular from 0.5 to 3.5% byweight, of rhodium,

[0020] from 0.05 to 5% by weight, in particular form 0.08 to 4.5% byweight, of zirconium,

[0021] from 0.1 to 3.5% by weight, in particular from 0.2 to 2.5% byweight, of iridium,

[0022] from 0.1 to 5% by weight, in particular from 0.2 to 1.5% byweight, of at least one metal selected from among copper, cobalt,nickel, manganese, iron, ruthenium and molybdenum,

[0023] from 0.05 to 5% by weight, in particular from 0.1 to 1.2% byweight, of at least one alkali metal or alkaline earth metal selectedfrom among lithium, sodium, potassium, rubidium, magnesium and calcium,on an inert support.

[0024] The catalyst of the present invention can be obtained byimpregnating the inert support with catalyst metal compounds, inparticular catalyst metal salts, dissolved in aqueous or organicsolvents, drying and calcining the impregnated support and subsequentlyreducing it. The impregnation can be carried out in any desired manner,for example by steeping or spraying. Preference is given to usingcatalyst metal salts which are soluble in water or organic solvents suchas ethanol. The order in which the support is impregnated with thecatalyst metal compounds can be chosen freely. Impregnation can becarried out successively or simultaneously with all components.

[0025] According to the present invention, the catalyst is used in thereaction of synthesis gas, in particular to give C₂-oxygenates such asethanol, acetaldehyde and acetic acid.

[0026] The reaction is preferably carried out at a pressure in the rangefrom 1 to 100 bar and at a temperature in the range from 200 to 400° C.

[0027] The molar ratio of H₂ to CO is preferably 10-0.05: 1.

[0028] The invention is illustrated by the examples below.

EXAMPLE 1

[0029] RhCl₃, ZrO(NO₃)₂, H₂IrCl₆, Cu(NO₃)₂ and KNO₃ were dissolved inwater in amounts corresponding to the desired concentration ratio on thesupport. The support (SiO_(2,) 20-40 μm) was then dipped into thesolution for from 1 to 2 hours. After removal from the solution andallowing excess solution to drip off, the support was dried at from 50to 60° C. for 24 hours and subsequently calcined at 110° C. for 6 hours.The catalyst obtained contained 1.5% by weight of Rh, 0.1% by weight ofZr, 0.3% by weight of Ir, 0.8% by weight of Cu and 0.2% by weight of K.

[0030] Prior to the reaction with synthesis gas, the catalyst wasreduced with hydrogen for 3 hours at 300° C. Synthesis gas was thenreacted at a temperature of 300° C. The total pressure of CO and H2 was3.0 MPa, the molar ratio of H₂/CO was 2. The space velocity was 15,000h⁻¹.

[0031] The CO conversion was 4.5%, the space-time yield of C₂-oxygenateswas 312.6 g/kg h. The selectivity was 70.1% of CO.

EXAMPLE 2

[0032] The same catalyst as in Example I was used, but in itspreparation the support was first dipped into ZrO(NO₃)₂ solution,subsequently dried and then dipped into a solution comprising RhCl₃,H₂IrCl₆, Cu(NO₃)₂ and KNO3. The catalyst was then dried.

[0033] The CO conversion was 4.3%, the space-time yield of C₂-oxygenateswas 351.2 g/kg h. The selectivity was 73.5% of CO.

EXAMPLES 3 to 11

[0034] The reaction was carried out as described in Example 1, but thecatalyst indicated in the following table was used. The results areshown in the following table. CO Space-time C₂-oxy conversion yield ofC₂- selectivity Example Catalyst % oxygenates % (C) 3 3.5 Rh-0.2 Zr- 8.7726.8 75.8 0.2 Ir-0.7 Cu- 0.1 Li/SiO₂ 4   1 Rh-0.08 Zr-0.5 Ir- 3.4 273.569.2 0.5 Mn-0.8 K- 0.1 Li/SiO₂ 5 1.5 Rh-0.1 Zr- 4.8 414.9 77.8 0.5Ir-0.2 Fe- 0.1 Ru-0.2 K/SiO₂ 6 2.0 Rh-0.1 Zr- 5.4 440.2 73.2 1.0 Ir-0.2Ru- 0.5 Li/SiO₂ 7 0.5 Rh-0.3 Zr- 2.1 148.6 63.7 0.8 Ir-0.9 Ru- 0.3 Mo-0.2 Mg/ZSM-5 8 1.0 Rh-2.8 Zr- 4.2 336.5 72.1 0.2 Ir-1.0 Mn- 0.5 Mo-1.2Li/SiO₂ 9 1.0 Rh-4.5 Zr- 3.9 340.2 78.5 0.5 Ir-0.5 Mn- 0.5 Cu-0.8 K/SiO₂10 1.0 Rh-0.3 Zr- 4.2 363.5 77.9 2.5 Ir-0.5 Mn- 0.2 K/SiO₂ 11 1.0 Rh-0.3Zr- 5.9 362.1 55.7 2.5 Ir-0.5 Mn- 0.2 K/Al₂O₃ C1 1.0 Rh-0.5 Mn- 1.2 96.765.3 0.2 K/SiO₂ C2 1.0 Rh-2.5 Ir-5 Mn- 3.9 289.4 66.8   2 K/SiO₂

We claim:
 1. A process for preparing C₂-oxygenates by reaction of CO andH₂ over a rhodium-containing supported catalyst, in which the catalystcomprises, based on the total weight, from 0.01 to 10% by weight ofrhodium, from 0.001 to 10% by weight of zirconium, from 0.01 to 5% byweight of iridium, from 0.01 to 10% by weight of at least one metalselected from among copper, cobalt, nickel, manganese, iron, rutheniumand molybdenum, from 0.01 to 10% by weight of at least one alkali metalor alkaline earth metal selected from among lithium, sodium, potassium,rubidium, magnesium and calcium, on an inert support.
 2. A process asclaimed in claim 1, wherein the catalyst support is selected from amongSiO_(2,) Al₂O₃, TiO₂, zeolites, activated carbon and diatomaceous earth.3. A process as claimed in claim 1 or 2, wherein the alkali or alkalineearth metal or metals is/are selected from among lithium, potassium andmagnesium.
 4. A process as claimed in any of claims 1 to 3, wherein themetal or metals is/are selected from among copper, manganese, iron,ruthenium and molybdenum.
 5. A process as claimed in any of claims 1 to4, wherein the reaction is carried out at a pressure in the range from 1to 100 bar and at a temperature in the range from 200 to 400° C.
 6. Aprocess as claimed in any of claims 1 to 5, wherein the molar ratio ofH₂ to CO is 10-0.05:1.
 7. A rhodium-containing supported catalystcomprising, based on the total weight, from 0.01 to 10% by weight ofrhodium, from 0.001 to 10% by weight of zirconium, from 0.01 to 5% byweight of iridium, from 0.01 to 10% by weight of at least one metalselected from among copper, cobalt, nickel, manganese, iron, rutheniumand molybdenum, from 0.01 to 10% by weight of at least one alkali metalor alkaline earth metal selected from among lithium, sodium, potassium,rubidium, magnesium and calcium, on an inert support.
 8. A process forpreparing a catalyst as claimed in claim 7, which comprises impregnatingthe inert support with catalyst metal compounds dissolved in aqueous ororganic solvents, drying and calcining the impregnated support andsubsequently reducing it. The use of a catalyst as claimed in claim 7 inthe reaction of synthesis gas.